This invention relates to fluids used in treating a subterranean formation. In particular, the invention relates to methods for treating subterranean formations including preparing an aqueous treatment fluid composition composed of a carboxy modified polymer, a crosslinking agent, and quaternary amine, then treating the subterranean formation with the fluid composition. The treatment method is particularly useful for fracturing a subterranean formation.
Various types of fluids are used in operations related to the development and completion of wells that penetrate subterranean formations, and to the production of gaseous and liquid hydrocarbons from natural reservoirs into such wells. These operations include perforating subterranean formations, fracturing subterranean formations, modifying the permeability of subterranean formations, or controlling the production of sand or water from subterranean formations. The fluids employed in these oilfield operations are known as drilling fluids, completion fluids, work-over fluids, packer fluids, fracturing fluids, stimulation fluids, conformance or permeability control fluids, consolidation fluids, and the like.
Hydraulic fracturing operation is a stimulation technique routinely performed on oil and gas wells to increase fluid production from subterranean reservoirs. Specially engineered fluids are pumped at high pressures and rates into the reservoir to be treated, causing a fracture to open. Proppants, such as ceramic beads or grains of sand, are slurried with the fracturing fluid (also referred to as carrier fluid) to keep the fracture open once the treatment is completed. Because of their low cost, high performance and ease of handling, polymer-based fluids are the most widely used fracturing fluids for hydraulic fracturing operations. Most commonly used polymers include guar, guar derivative, cellulose, and cellulose derivative based polymers.
In some instances, polymers used to form the fluid are crosslinked with a crosslinker, such as titanium, boron, or zirconium, in order to provide adequate viscosity to hydraulically fracture the formation. Often, when some crosslinked polymer fluids are pumped into a wellbore to treat the formation, as a result of exposure to pumping and transport forces, the fluids may exhibit shear thinning behavior with limited or no viscosity recovery when the shear rate is decreased. This is especially the case with zirconium crosslinked polymer based systems. Such shear thinning behavior commonly leads to significant leak-off of the treatment fluid into the formation
A typical approach to partially alleviate irreversible shear thinning effects is increasing the crosslinked polymer concentration of the treatment fluid. While this may be effective for improving viscosity, this may lead to other difficulties. Generally, as polymer levels are increased, material requirements increase as well. Further, elevating the polymer concentration commonly leads to a corresponding reduction in retained conductivity after the treatment operation.
Thus the need exists for oilfield treatment fluids which provide high retained conductivity after treatment, as well as improved viscosity recovery after shear thinning. A fluid that can achieve this would be highly desirable, and these needs are met at least in part by the following invention.